Hi. I'm also getting into pentesting so I'll just let you know what I've tried and my experiences with 'em.
Dual boot: I don't know how well versed in linux you are, but I found it easier to just use the programs that work in windows, then ftp-ing the things over to my VMWare BT5. If you have a powerful enough machine, (mine is i7 sec gen 2820 QM w/ 8 gig ddr 3 ram), then the speed gain of a separate OS is not a real factor.
Virtual Machine: I love this. I can use my tools, while looking up things on windows, use the windows OS as a separate workhorse, and run everything easily in windows then, like I said, ftp the results over to BT5. I had to split a 10.7 gig wordlist. In BT, hours. In windows splitting + ftp-ing - 15 minutes. CONS: Unless you set up a bridged network, which currently I'm having trouble with, you wont be able to run tools like ettercap, AIRSSL, arpspoof,.... because it won't be able to connect with it's own IP. Annoying, but if I find a solution or someone helps me, then definitely, in my opinion, the way to go.
Main OS: Good luck. That's dedication.